ATSHA204A datasheet(59/93 Pages) MICROCHIP

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The Pause command differs from the idle flag/sequence in that individual devices on the single pin bus

may be selected to go into the idle state, as opposed to the idle flag which causes all the

CryptoAuthentication devices on the bus into the idle state.

If the EEPROM Selector byte does not match the input selector parameter, the device immediately goes

to the idle state. If the input selector parameter does match the configuration selector byte, the device

returns a success code of 0x00.

The Pause command cannot be used to put the devices into the sleep state.

Table 8-28. Input Parameters

Name

Size

Notes

Opcode

Pause

0x01.

Param1

Selector

All devices that do not match this value go to idle state.

Param2

Zero

Must be 0x0000.

Data

—

Table 8-29. Output Parameter

Name

Size Notes

Success

If the command indicates that some other device should idle, the ATSHA204A returns a value of

0x00.

If this device goes to idle, no value is returned.

8.5.14

Random Command

The Random command generates a random number for use by the system.

Random numbers are generated through a combination of the output of a hardware RNG and an internal

seed value stored in the EEPROM or SRAM. The external system may choose to update the internally

stored EEPROM seed value prior to the generation of the random number as part of the execution of the

Nonce or Random command, for highest security, Microchip recommends that the EEPROM seed

always be updated.

The Random command does not provide a mechanism to integrate an input number with the internal

stored seed. If this functionality is desired, the system should use the Nonce command and ignore the

generated nonce.

Prior to the configuration section being locked, the RNG produces a 32 byte value of 0xFF, 0xFF,

0x00, 0x00, 0xFF, 0xFF, 0x00, 0x00... to facilitate testing.

The same internally stored seeds are used for both the Nonce and Random commands. Use of

Mode<0> ensures that the EEPROM is updated, if necessary.

Table 8-30. Input Parameters

Name

Size

Notes

Opcode

Random

0x1B.

Param1

Mode

Controls the mechanism of the internal RNG and seed update.

ATSHA204A

Security Commands

DS40002025A-page 59

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